What does your fstab say (with hda1 mounted)?

I can't answer specifically for NTFS partitions, but partitions are mounted read only on purpose. In order to write to a partition, you need to unmount it, then remount it so its writeable.

umount hda1 should unmount it.

First, make sure you have everything closed that was accessing the partition. If you have konqueror open, for example, and were browsing the partition, you'll get an error message that says that the partition can't be unmounted, its in use. Close konqueror (or just the tab that you were browsing the partition with), and you should then be able to unmount. If you still can't unmount, type:
fuser -m /dev/hda1

and that will tell you the process numbers of the applications that are still using the partition. If there aren't any, then try typing:

umount -l hda1

and that should work in a just a couple of seconds.

Once the partition is unmounted, then you mount it, with the writeable flag,

mount -o rw hda1
or
mount -w hda1

may work, or

mount -w -t ntfs hda1

may work.

After trying one of the above, you may be able to write to the partition only while logged on as root. If that is the case, then you need to change the uid, gid, and umask settings in fstab. You can google for the correct settings if that is the case. And if this is the case, your partition is correctly mounted as writeable, you just need to change permissions as indicated in the previous sentence.

I don't have any ntfs partitions, so the above is without warranty, and I'm not responsible if you damage your system. You should wait for someone else to post their solution, as I know there are issues with writing to ntfs (it wasn't even possible in earlier versions of knoppix, or any earlier Linux distros). Always backup first.

Also look at man mount, man unmount. Also, if there are other users on the system, it is possible to change the flag to writeable on a partition without unmounting it, man mount should have that info, I don't know how reliable/safe it is to do so.